Working With Galvanized Pipe

You will find galvanized pipe in many older homes used as water supply lines. Galvanized is not used for gas lines, as the zinc used in making galvanized pipe will flake off and clog the supply system. Although galvanized pipe is not used in new builds any longer, it is used in hand rails and replacement of existing pipe. A working knowledge of galvanized pipe is needed for the do-it-yourselfer who lives in an older home or does repair work for people that do.

What Is Galvanized Pipe?

Galvanized pipe was used extensively in homes that are now over 30 years old. It was originally used as water supply lines. It is steel pipe that is covered with a layer of zinc to increase life expectancy and avoid corrosion. Galvanized pipe has a tendency to react with the minerals in the water it carries, producing scale that can lead to lower water pressure. Hard water in the home generally reduces the life expectancy of galvanized pipe. It was also used in drains and vents in older homes. Galvanized nipples are still used to penetrate fire rated walls for sinks and urinals.

It is best to check with the local department of public works to find out the PH level of the water in your locale. If you have a well on your property, have a sample of water tested. Low PH, below 6.5, is hard on copper. This is a good reason for using galvanized pipe.

Installing Galvanized Pipe

Galvanized is installed in much the same way as black iron pipe. The pipe comes in standard lengths of 21 feet. Hold the pipe for cutting in a pipe vise, or a good solid bench vise. Cut the pipe to length using a pipe cutter with rotary cutting wheels. Use quality cutting oil in this process. Always wear gloves when working with pipe.

TIP:Doityourself’s plumbing consultant Wayne McCarthy suggests, “Make sure you have a large piece of cardboard or plywood under your cutting and threading area. This will save you a lot of cleaning later.”

Once it is cut to length, deburr the interior of the pipe to remove the sharp ridge caused by the cutting process.

With the pipe still held in the pipe vise, thread the end of the pipe with a die cutter, ensuring you have the correct size for the diameter of the pipe. Once again, use a good cutting oil to prevent damage to the die and ease the process. Turn the die on in half-turn strokes, backing off every turn to dislodge shavings from the die. Cut the thread to the width of the die. Because the thread is tapered, going farther will remove too much of the pipe, causing possible leakage. Tap out shavings from the pipe and clean the threads. Be careful that you do not cut yourself on the threads -- they are very sharp.

TIP:Wayne adds, “You can buy a ratchet type threader for around $30 at discount tool places that will handle pipe up to 1-inch. As most places charge $5 or more to cut one thread, this might be more economical in the end. Use a lot of cutting oil and catch it in a bucket with a large screen or strainer over it. This will prevent damage to the cutter and the threads, and also allow you to re-use the oil. Backing the die off the threads is not necessary unless the threading die binds. Then back it off about one half turn and continue. To test your threads use a factory threaded end in a fitting and see where it snugs-up. Then cut one on your own and judge your threads from there.”

Joining the Pipe

Galvanized pipe is joined using fittings made of malleable cast iron. They are threaded onto the pipe to make the connection. Use Teflon tape and a good quality pipe joint compound when attaching. Once the pipe is installed, turn on the water supply and check for leaks. If leaks are present, retighten any joints.

TIP:Wayne says, “Make sure you are wrapping the Teflon tape in the right direction. Facing the end of the pipe you go in a clockwise direction with at least 4 wraps but no more than 6 or 7. Then apply some pipe dope in the same direction. Tighten at least 2 turns past hand tight and if the pipe is still loose you may have to re-cut the pipe.”

Hanging the Pipe

Because galvanized pipe is very heavy, it needs proper support. Undue stress on connections from the weight can lead to leakage. Support the pipe every 6 feet minimum if run along a floor joist. You can use pipe hanging straps or use regular pipe hangers if the pipe is close the support. Vertical runs should be supported at every floor level.

TIP:Wayne adds, “A good rule of thumb for supports is every 6 to 8 feet on horizontal piping. If you do have a leak, even us pros get them, you may have to take some things apart to fix the leak. Do not try to tighten a joint in the middle of a run as you are also loosening the joint on the other end.”

Joining Galvanized Pipe with Copper

In case of leakage, galvanized pipe can be joined with copper. This is done with a dielectric union. The reaction between copper and galvanized leads to corrosion very quickly, and the dielectric union eliminates this. The two metals are effectively separated by a rubber washer.

Remove the old leaking joint. Cut the pipe with a hacksaw near the joint. Using pipe wrenches, work back to the next nearest joint, working in both directions. Check the galvanized to see if it is badly clogged with mineral buildup. If so, keep working backward until you find pipe that is not clogged.

Next, thread the galvanized pipe into the dielectric union, using pipe joint compound. Uncouple the union, and solder the copper replacement pipe onto the union. Reattach, tightening well to avoid leakage.

The down side to this situation is if you find one clogged pipe and a leaking joint, the chances are good that the entire system needs replacing. However, using a dielectric union will often fix the issue for a long period of time.

Other Uses

Galvanized is ideal for outdoor railings. Floor flanges are made for attachment and you can use the same malleable connectors to join the lengths.

TIP:Wayne suggests, “When using Galvanized pipe for railings use stainless anchors for anchoring in concrete as they will last longer.”

Wayne McCarthy, professional plumber, contributed to this article.